If else multiple tuples in a list-CodePudding

I am having an if method to check whether the [1] index value inside a tuple is less or equal to 255. While im feeding this method a single tuple inside a list it works eg [(0, 323)], but when im feeding the [(0, 323), (1, 1)] it doesn't.

if [i for i in a if i[1] <= 255]:
    print("a")
else:
    print("b")

Example if my values are [(0, 323)] it correctly prints b but when they change to a multiple tuple inside the same list [(0, 323), (1, 1)] it just prints a which is not correct. Any inputs please?

CodePudding user response：

Example if my values are [(0, 323)] it correctly prints b but when they change to a multiple tuple inside the same list [(0, 323), (1, 1)] it just prints a which is not correct. Any inputs please?

The behaviour is perfectly in line with the code:

[i for i in a if i[1] <= 255]

will return a list of all the tuples where the second item is under 255. For your second test case it returns [(1, 1)].

This is then interpreted in a boolean context, in Python collections are generally "truthy" if the collection is non-empty and "falsy" is empty. A list of one element is non-empty, therefore truthy, therefore "a".

If you want this to pass when all tuples have a second value under 255, then that's a job for... the all function.

# transform the comprehension because `all([])` is `True` which seems
# undesirable here
if all(thing <= 255 for _, thing in a):
    print("a")
else:
    print("b")

Incidentally, i is colloquially an index, since this is not the case here i should be avoided. Same with j.

For a genering element prefer e, or better provide a name which actually explains what the thing is.

CodePudding user response：

You are currently checking if there is ANY tuple in the list whose second item is less or equal to one. If that's what you want, any() would be better:

if any(each for each in a if each[1] <= 255):
    print("Yup, at least one tuple matched")
else:
    print("Nope, not a single one")

If you want to check if all the tuples matches, you use all().

If you want to check each item, you need to loop over the list:

for each in a:
    if each[1] <= 255:
        print(f"{each} matches")
    else:
        print(f"{each} does not match")